Two Maryland men working at a Southeast Washington construction site were killed yesterday when walls of dirt and mud collapsed around them.

District of Columbia police said Jeff Mattingly, 28, of 5415 55th Pl. in East Riverdale, and Dan Bowen, 32, of 7515 Buchanan St. in Landover, were hooking up sewer pipes at the High View town house project, on Barnaby Terrace in Southeast Washington, when the walls caved in shortly before noon. The two men were employes of George F. Warner and Co. of Northeast Washington.

The D.C. police department's homicide division, the city's labor department and the federal Occupation Safety and Health Administration are conducting investigations of the deaths.

John Jackson, safety inspector with the D.C. Occupational Safety and Health Administration, said yesterdat that there was no evidence the men had shored up the sides of the excavation before beginning their work.

The investigation probably will bot be completed for more than a week, Jackson said.

Jackson said city and federal OSHA inspectors are supposed to inspect construction sites regularly and make certain construction workers are informed about safety regulations.

A.D.C. Fire Department spokesman said sometimes construction companies do not shore up excavation sites. "It's something done to beat the cost," the spokesman said, "It 's quicker. If you do it and can get away with it, then it's okay. If you don't, you lose a life. That's what happened here today."

Police officials said they had been told there was a partial cave-in at the same site Monday.

Officials at Warner company said they would have no statement to make on the incident until they finish their investigation.

Mattingly and Bowen apparently were buried under about four feet of dirt and mud. The excavation site was 20 feet deep and 15 feet long.

Police officer Michael C. Vincent and workmen at the site tried to dig the two trapped men out and shore up the hole with siding. When fire and safety officials arrived, however, they made the men stop digging until everything was shored be trapped. About 40 firemen helped with the shoring.